1. Field of the Invention
This invention is directed to a multi-channel audio playback device and method, and more particularly to a device and method adapted to characterize a multi-channel loudspeaker configuration and correct loudspeaker/room delay, gain and frequency response.
2. Description of the Related Art
Home entertainment systems have moved from simple stereo systems to multi-channel audio systems, such as surround sound systems and more recently 3D sound systems, and to systems with video displays. Although these home entertainment systems have improved, room acoustics still suffer from deficiencies such as sound distortion caused by reflections from surfaces in a room and/or non-uniform placement of loudspeakers in relation to a listener. Because home entertainment systems are widely used in homes, improvement of acoustics in a room is a concern for home entertainment system users to better enjoy their preferred listening environment.
“Surround sound” is a term used in audio engineering to refer to sound reproduction systems that use multiple channels and speakers to provide a listener positioned between the speakers with a simulated placement of sound sources. Sound can be reproduced with a different delay and at different intensities through one or more of the speakers to “surround” the listener with sound sources and thereby create a more interesting or realistic listening experience. A traditional surround sound system includes a two-dimensional configuration of speakers e.g. front, center, back and possibly side. The more recent 3D sound systems include a three-dimensional configuration of speakers. For example, the configuration may include high and low front, center, back or side speakers. As used herein a multi-channel speaker configuration encompasses stereo, surround sound and 3D sound systems.
Multi-channel surround sound is employed in movie theater and home theater applications. In one common configuration, the listener in a home theater is surrounded by five speakers instead of the two speakers used in a traditional home stereo system. Of the five speakers, three are placed in the front of the room, with the remaining two surround speakers located to the rear or sides (THX® dipolar) of the listening/viewing position. A new configuration is to use a “sound bar” that comprises multiple speakers that can simulate the surround sound experience. Among the various surround sound formats in use today, Dolby Surround® is the original surround format, developed in the early 1970's for movie theaters. Dolby Digital® made its debut in 1996. Dolby Digital® is a digital format with six discrete audio channels and overcomes certain limitations of Dolby Surround® that relies on a matrix system that combines four audio channels into two channels to be stored on the recording media. Dolby Digital® is also called a 5.1-channel format and was universally adopted several years ago for film-sound recording. Another format in use today is DTS Digital Surround™ that offers higher audio quality than Dolby Digital® (1,411,200 versus 384,000 bits per second) as well as many different speaker configurations e.g. 5.1, 6.1, 7.1, 11.2 etc. and variations thereof e.g. 7.1 Front Wide, Front Height, Center Overhead, Side Height or Center Height. For example, DTS-HD® supports seven different 7.1 channel configurations on Blu-Ray® discs.
The audio/video preamplifier (or A/V controller or A/V receiver) handles the job of decoding the two-channel Dolby Surround®, Dolby Digital®, or DTS Digital Surround™ or DTS-HD® signal into the respective separate channels. The A/V preamplifier output provides six line level signals for the left, center, right, left surround, right surround, and subwoofer channels, respectively. These separate outputs are fed to a multiple-channel power amplifier or as is the case with an integrated receiver, are internally amplified, to drive the home-theater loudspeaker system.
Manually setting up and fine-tuning the A/V preamplifier for best performance can be demanding. After connecting a home-theater system according to the owners' manuals, the preamplifier or receiver for the loudspeaker setup have to be configured. For example, the A/V preamplifier must know the specific surround sound speaker configuration in use. In many cases the A/V preamplifier only supports a default output configuration, if the user cannot place the 5.1 or 7.1 speakers at those locations he or she is simply out of luck. A few high-end A/V preamplifiers support multiple 7.1 configurations and let the user select from a menu the appropriate configuration for the room. In addition, the loudness of each of the audio channels (the actual number of channels being determined by the specific surround sound format in use) should be individually set to provide an overall balance in the volume from the loudspeakers. This process begins by producing a “test signal” in the form of noise sequentially from each speaker and adjusting the volume of each speaker independently at the listening/viewing position. The recommended tool for this task is the Sound Pressure Level (SPL) meter. This provides compensation for different loudspeaker sensitivities, listening-room acoustics, and loudspeaker placements. Other factors, such as an asymmetric listening space and/or angled viewing area, windows, archways and sloped ceilings, can make calibration much more complicated
It would therefore be desirable to provide a system and process that automatically calibrates a multi-channel sound system by adjusting the frequency response, amplitude response and time response of each audio channel. It is moreover desirable that the process can be performed during the normal operation of the surround sound system without disturbing the listener.
U.S. Pat. No. 7,158,643 entitled “Auto-Calibrating Surround System” describes one approach that allows automatic and independent calibration and adjustment of the frequency, amplitude and time response of each channel of the surround sound system. The system generates a test signal that is played through the speakers and recorded by the microphone. The system processor correlates the received sound signal with the test signal and determines from the correlated signals a whitened response. U.S. patent publication no. 2007,0121955 entitled “Room Acoustics Correction Device” describes a similar approach.